A lithium-ion secondary battery has a structure in which a positive electrode material applied to aluminum foil and a negative electrode material applied to copper foil face each other via an insulating porous polyethylene film so as not to make electrical contact, and the interior space is filled with an electrolytic solution in which a non-aqueous electrolyte such as a carbonate ester and additives have been dissolved. Fluoride-based electrolytes with good characteristics in terms of conductivity, potential window, and interaction with metals are often used as electrolytes in lithium-ion secondary batteries. However, hydrolysis of these fluorides releases hydrogen fluoride, and this hydrogen fluoride dissolves the electrode materials and corrodes the current collector. These problems cause battery performance to deteriorate.
In order to address these problems, the conventional method is to prevent contamination by water in the manufacturing process, thereby inhibiting the hydrolysis of fluoride-based electrolytes. However, it is difficult to completely prevent contamination by water in the manufacturing process using the conventional method, so the creation of hydrogen fluoride in the electrolytic solution cannot be completely prevented. In addition to during manufacture of the electrolytic solution, water contamination is also known to occur during shipment of the electrolyte and during manufacture of batteries. In order to reduce contamination by water, manufacturing has to be performed in a controlled environment where humidity is reduced such as in a dry room, and this increases production costs.
In order to prevent hydrogen fluoride generated by hydrolysis from adversely affecting a non-aqueous electrolyte, the inclusion of a compound for adsorbing hydrogen fluoride in the electrolyte and/or electrode materials has been proposed. Among these, synthetic hydrotalcites known as intercalated materials (Patent Document 1) and organically synthesized hydrotalcites (Patent Document 2) have been proposed as superior hydrogen fluoride removing materials. These hydrotalcite compounds have a layered structure, and act to adsorb and fix hydrogen fluoride molecules and sometimes water molecules between layers.